1. Field of Invention
The present invention generally relates to container manufacturing machines and, in particular, to feed mechanisms for container manufacturing machines.
2. Description of the Related Art
Containers are processed within machines that may perform one or several processes. Attempts by many in the industry have been made to make containers in one machine by combining multiple processes within a single entity defined by discrete separation and transport mechanisms. Differing process requirements, cycle times or progressive geometry changes in the article have prevented this from being achieved.
Containers have to be transported from one process machine to the next and then, in many cases, presented to the processing element of the machine as a discrete unit. In the manufacturing of two piece cans, for example, it is usual to flow containers to the machine in a single file at speeds of up to 2800 per minute. For a typical beer or beverage can having a diameter of 2.60 inches, this translates to a conveying speed of 10 feet per second.
During transport from process machine to process machine, the cans are typically in contact with each other. However, for processing in the machines, the cans have to be separated and moved further apart. This is because the mechanical process components need space to operate on individual cans. Machine designers strive to minimize this space, or pitch, but it is typically in excess of 6.0 inches and may be as large as 8.75 for some machines.
Cans arriving at a process machine without sufficient pitch, may be dented during separation. Dents are bad because they weaken the can. In order to maintain adequate strength for further processing, excess metal has to be used to compensate for the denting. As 65% of the cost of the can is the metal, minimizing dents is important. Separating the cans so that they can be processed in a controlled manner and with no damage has become increasingly difficult as cans have become thinner and speeds increased. Within the infeed of a machine, cans are accelerated to between 150% and 350% of their delivery speed in a few milliseconds.
Typical early process machinery for feeding cans used either an indexing process or continuous rotary motions. For an indexing machine, one could use a tick-tock gate or the turret periphery to meter product into the machine feed turret or main process turret from a gravity feed track. Additionally, a tick-tock gate or the turret periphery could be used to meter rope, belt, chain, magnetic, air or vacuum feed conveyors.
A conventional gravity feed mechanism for a trimmer is illustrated in FIG. 1. The Trimmer 1 has two gravity fed infeed chutes 3. Each infeed chute 3 delivers cans directly to a process turret 5. The cans are trimmed and then exit on conveyor 7.
Indexing limited throughput to about 350 cans per minute (cpm) and caused a low feed velocity. Continuous rotary motion enabled progressively faster speeds but conventional wisdom held speeds below 100 cpm per working pocket. For a machine to be rated at 800 cpm it needed at least 8 working pockets.
A preferred separation and timing device used in the prior art was the Feed Screw, illustrated in FIG. 2. This was a typically 3xe2x80x3 diameter screw 21 with a progressive helix matching the outside diameter of the can. The initial lead pitch was the same as the can diameter and the final pitch matched the tangent velocity of the pitch line of the feed turret 23 of the machine. The can was fed from the screw 21 into a pocket 22 of feed turret 23. The tip 24 of the pocket 22 cupped the can as the can moved toward the main turret 25. The can was passed to the main turret 25, trimmed and exited through the discharge chute 27. The energy to accelerate and separate the cans comes from gravity or a driving conveyor running under the base of the cans at least as fast as the pitch-line velocity of the turret. The screw is used to hold back and meter the cans in a controlled way.
The Feed Screw was also considered a random feed device. A second process machine was operated continuously at a constant speed that was faster than the machine before it. This resulted in gaps in the product flow. The first can of the next xe2x80x9cstickxe2x80x9d (column of cans) was fed at random into the in-running nip of the screw 21 where it sometimes bounced around, getting dented, until there was enough pressure from behind to force it in. Other feed techniques used included mechanically complex advancing starwheel pockets or sweeper arms to meter cans to the starwheel.
Coors introduced a Constant Velocity starwheel on their 1975 LAG 75 Necker/Flangere(copyright), designed for 1200 cpm (FIG. 6). The 12 pocket turret 63 had a 13.5xe2x80x3 pitch can diameter (where the pitch can radius 68 is measured from the center of the turret to the center of the can and the locus of pitch can diameters defines a pitch circle 64), so pocket separation was only 3.5xe2x80x3. Cans 62 coming in were metered and separated by a combination of a curved infeed track 61 and a cam form 69 on the trailing side of the hooked starwheel pocket 65. The geometry maintained a constant speed of flow in the can stack during the stripping of each can 62, hence the name. In the LAG 75(copyright) machines, there were no infeed mechanisms at all. Cans 62 fed directly into the main process turret 63. A gravity chute 61 linked the process turrets 63 with a timed can stop maintaining the stack height.
If the combination of a curved infeed track 61 and a cam form 69 on the trailing side of the hooked starwheel pocket 65 is used in a direct turret to turret transfer within a machine, the profile of the pockets has to be truncated at the pitch line 64. This is necessary in order to prevent the tip xe2x80x9chookingxe2x80x9d through the can as it is transported away by the subsequent turret. This is illustrated in FIG. 6 at numeral 66. Additionally, the hook 65 supports the stack early and does not reverse the flow of the cans 62 (illustrated at numeral 67).
The final evolution of this system was the 595 Super K(copyright) (FIG. 7). It uses a slightly modified path geometry for 3000 cpm capability feed into a vacuum infeed turret 73 with 12 pockets and 13.5xe2x80x3 pitch can diameter (pitch circle 74). The main turret 75 also has a 13.5xe2x80x3 pitch can diameter (pitch circle 76). Thus, the pitch circles 74, 76 are interfacing. The infeed turret 73 has truncated hooked pockets 77 which facilitate transfer of cans from interfacing turrets (illustrated at numeral 79).
Belvac used a modified constant velocity (CV) path geometry in trimmers which, by necessity, run at sub-500 cpm speeds. The constant velocity infeed starwheel was introduced in 1985 to eliminate a complex tic-toc metering and stop mechanism.
A CC93(copyright) constant velocity infeed is illustrated in FIG. 3. Cans were gravity fed in the infeed chute 31. A pneumatic stop 32 was used to interrupt the flow of the cans into the infeed starwheel 33 as the head was depleted. Cans were then passed from the infeed starwheel 33 to the main turret 36 via the infeed gate 35. The CC93(copyright) infeed also included a timing mechanism 34 to aid in controlling the pneumatic stop. After trinnig, the cans entered an outfeed chute 37. Scrap material exited through scrap duct 38.
The present invention provides a feed mechanism for feeding containers including: an infeed starwheel and a main turret starwheel, wherein the pitch line of the infeed starwheel and the pitch line of the main turret starwheel are non-interfacing.
The present invention also provides a feed mechanism for feeding containers including: an infeed starwheel, a main turret starwheel and a feed chute with at least one hump for dissipating the head pressure of the incoming can stack.
The present invention also provides a method of feeding cans to a unit operation in a can making process including: providing a feed chute adapted for gravity feeding said unit operation, the feed chute having a top end and a bottom end, wherein the feed chute has a hump proximal to the bottom end and disposing a plurality of cans in the feed chute, thereby forming a stack of cans in the feed chute.